Corrosion of pipelines is a concern for the oil industry. It has become clear that corrosion in water injection pipelines is to a large extent caused by H2S-producing bacteria. This phenomenon is commonly referred to as microbially-induced corrosion (MIC).
Some of the bacteria responsible for corrosion belong to a group of sulphate-reducing bacteria (SRB), which are active under anaerobic conditions. Sulphate-reducing bacteria convert sulphate (SO42−) to hydrogen sulphide (H2S). SRB's can be found in almost all natural environments such as soils, fresh and marine waters, hot springs, geothermal areas, oil and gas wells, and in sewage systems.
In addition to induced corrosion of surface facilities, production of H2S causes reservoir souring requiring additional safety precautions at the production side. Consequently, there is a need to reduce the H2S production in a reservoir setting.
The sulphate-reducing bacteria are sessile, i.e. they grow on surfaces, and protect themselves by forming biofilms, which cause bio-fouling if not properly removed. Inhibiting the growth of SRB's and other H2S-producing bacteria is therefore a matter of importance for the oil industry.
In the oil industry, pipelines may be cleaned mechanically by pigging the pipeline. This involves inserting a device (called a pig) with blades or brushes in a pipeline for cleaning purposes. The pressure of a stream of oil or water behind pushes the pig along the pipeline to clean out rust, wax, scale, and debris such as biofilms. Pigging the pipeline is only partly effective in reducing the H2S-producing bacteria.
In the oil industry, cleaning of pipelines have been attempted chemically by adding commercial biocides such as formaldehyde, glutaraldehyde or tetrakishydroxymethyl phosphonium sulphate (THPS) are, or have been, used in water injection pipelines to inhibit growth of microorganisms. These chemicals are typically expensive, can be dangerous to handle, may have a negative impact on the environment and are only partially efficient in controlling bacterial growth in biofilms.
In the oil industry, cleaning of pipelines have been attempted biologically as described in U.S. Pat. No. 8,168,419 (to Baldwin et al.), which discloses prevention and remediation of petroleum reservoir souring and corrosion by treatment with virulent bacteriophage. A bacteriophage (phage) is a virus, which infects only prokaryotic cells (cells without a nucleus), such as bacteria, while leaving mammalian (e.g. human) cells unharmed. These bacteriophages must be adapted to the specific type of bacteria that is to be removed.
Finally, cleaning drinking water has been attempted using radiation. Treatment of drinking water with ultraviolet (UV) light is a method, which has been in use since 1955. More recently, it has been adopted by the oil industry during hydraulic fracturing operations, see Neal et al. “Nonchemical Bacteria-Control Process” (2010) SPE 133368. The bacteria will absorb UV light causing their DNA to undergo physical changes preventing further cell replication. While treatment with UV light is a non-chemical disinfection method, it suffers the drawback that in order to be effective the water has to be clear without any suspended solids or hydrocarbons for this mechanism to have optimum effect. Furthermore, UV radiation has not been deployed on a continuous basis.
Accordingly, there exists a need in the art for overcoming one or more of the deficiencies described in the prior art.